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  1. #1
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    Load Development for an SBR

    As we all know I am building my SBR but yesterday the conversation turned to building a load for that type of rifle.

    There is a lot of talk about dwell time and all that when talking about shorter barrels (mine is 10.5 with a 1/7 twist)...

    I have done some google fu and with a standard 55 grain bullet muzzle velocity will be around 2500 fps out of a 10.5 barrel.

    In my 16" rifle I am getting around 2600 fps with 69 grain SMKs. So just doing the math here (in theory) that if I shot my current loads through a 10.5 barrel my muzzle velocity would be down to under 2000 fps.

    That said wouldn't that increase dwell time? Really though that's not my question or point of discussion... I am assuming that all these loads would run flawlessly through the gun....

    On the flip side if I go with a lighter projectile I get my velocity up substantially but there are obviously trade offs to doing this.

    On the really light side you have 40 grain bullets... and on the heavy side you have 77 grain bullets...

    Basically considering that I am talking 200 yards tops so the real long range benefits of a 77 grain is kind of negated as to ballistics. That said I am of the school that more lead the better.

    Basically it would boil down to what would be equivalent to a light load with a 77 grain (or other heavy round) or a faster load with a lighter projectile.

    I also have a little bit faster burning of a powder that I am going to experiment with (H4895)

    After thinking it over it might be best to go somewhere in the middle...a 55 or 62 grain bullet...but I am not really sure.

    What do you reloaders think?

    The end result is to be able to have an accuratized and effective load that is built for my gun. Also mainly I can reload fast and cheap...to get that consistent load...

    Any ideas???

    Molon, Molon! Where are you at bro!!!

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    Generally speaking, you pick the bullet weight off the barrel twist rate. The faster the twist rate, the heavier the bullet,

    In an ideal world, you pick the barrel based on the bullet you will be shooting. There are formulas out there for matching up the barrel twist rate and bullet specifics...https://en.wikipedia.org/wiki/Miller_twist_rule. *Note that barrel length is not a determining factor.

    Even with the "ideal" bullet weight/twist rate calculated, your barrel may still like different grain bullets more or less.

    ***Hopefully Molon will respond...I'm sure his explanation/recommendations will be better than mine!

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    Sorry, didn't see where you had posted the twist rate. Honestly I'd go with 77gr. For the best accuracy, perform a ladder test to determine the sweet spot for your specific combination of bullet, powder, and barrel.

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    If it's straight up on twist rate that's one thing... it cuts down the hunt quite a bit for a suitable projectile. Maybe I was just doing my regular bit of over thinking... on a regular rifle it pretty much all makes sense to me. With an SBR though I got to wondering about velocity and all that stuff too.

    If I go with the 75 grains based on the hogdon reload data and a little bit of guesswork I would be right around 2000 fps. I just kind of wonder if that would matter...Of course I wouldn't want to get shot with it.

    I punched all that into a ballistics calculator and it would seem alright for the purpose intended...especially considering it's a 1x optic.

    I am having to kind of fight my nature to go for accuracy for long range and all that. Accuracy yes... but in this case out to 200 yards I am pretty sure I would be doing ok.

    I just wonder if a low velocity 75 grain shot would be more destructive than a faster 55 grain...

  5. #5
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    I wonder what this video would look like with a 75 or 77 grain bullet....

    (Watch below)

    https://www.youtube.com/watch?v=6CYq3t0rC_I

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    77gr otm works wonders.

    3inch group at 100y in my 7.75 inch pws mk107 upper.

    Its seriously an awesome round.

    Does cool stuff to people too.

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    Quote Originally Posted by voodoo_man View Post
    77gr otm works wonders.

    3inch group at 100y in my 7.75 inch pws mk107 upper.

    Its seriously an awesome round.

    Does cool stuff to people too.
    I will take your word for it when it comes to 'cool stuff to people' LOL!

    Just knowing me if it can be made accurate it will be made accurate It's just one of the things I am better at doing. It takes a certain level of nerdiness to make it be right on zero. That said to be honest I am specifically NOT looking for dime size groups at 100 yards... it would be nice to do it but it's not the point behind the build.

    That said for a gun that is designed like my SBR is designed bullet/round design matters but it has an entirely different aspect to it.

    So far there have been several people saying go heavy. I was just kind of at a loss on what that would do considering the velocity loss (or exactly what kind of loss that would be)...

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    Are you loading just for accuracy, or are you also loading for terminal ballistic properties? Extensive testing done at Lake City decades ago determined that 60% of the cartridge accuracy was determined by the bullet.

    So, if you are loading strictly for accuracy, the first thing you need to do is find a bullet that shoots well from your barrel.

    EVERY BARREL IS A LAW UNTO ITSELF. (So say we all!)

    What shoots well from my barrels, might not shoot well from your barrels. Also, twist rate only determines the gyroscopic stability factor of a bullet fired from a particular barrel. Twist rate will not determine what weight bullet will shoot the most accurately from your barrel. (Of course you must have enough twist to produce the minimum necessary amount of gyroscopic stability for a given bullet.)

    I've owned several 1:7" twist barrels that shot slightly more accurately with 55 grain bullets than they did with 75-77 grain bullets. Since you stated that you would only be shooting to approximately to 200 yards you might not necessarily need the higher ballistic coefficient of the heaver/longer bullets, but that also doesn't mean that one of the heavier/longer bullets won't be the one to shoot the most accurately in your barrel, even at shorter distances.

    One of the smallest 10-groups that I've fired from a semi-automatic AR-15 at a distance of 100 yards had an extreme spread of 0.428". The bullet used was the Barnes 85 grain Match Burner.







    Another small 10-shot group fired from a semi-automatic AR-15 at a distance of 100 yards had an extreme spread of 0.474". The group was fired using Sierra 55 grain BlitzKings.





    Both of the groups pictured above were fired from barrels with 1:7.7" twists.


    So find a bullet that your barrel likes, and then you can start making adjustments with different charges of different burning rate powders.

    If you're loading for terminal ballistic properties, that's a whole nother ball game.
    Last edited by Molon; 20 December 2015 at 19:30.

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    Quote Originally Posted by Molon View Post
    Are you loading just for accuracy, or are you also loading for terminal ballistic properties? Extensive testing done at Lake City decades ago determined that 60% of the cartridge accuracy was determined by the bullet.

    So, if you are loading strictly for accuracy, the first thing you need to do is find a bullet that shoots well from your barrel.

    EVERY BARREL IS A LAW UNTO ITSELF. (So say we all!)

    What shoots well from my barrels, might not shoot well from your barrels. Also, twist rate only determines the gyroscopic stability factor of a bullet fired from a particular barrel. Twist rate will not determine what weight bullet will shoot the most accurately from your barrel. (Of course you must have enough twist to produce the minimum necessary amount of gyroscopic stability for a given bullet.)

    I've owned severl 1:7" twist barrels that shot slightly more accurately with 55 grain bullets than they did with 75-77 grain bullets. Since you stated that you would only be shooting to approximately to 200 yards you might not necessarily need the higher ballistic coefficeint of the heaver/longer bullets, but that also doesn't mean that one of the heavier/longer bullets won't be the one to shoot the most accurately in your barrel, even at shorter distances.

    One of the smallest 10-groups that I've fired from a semi-automatic AR-15 at a distance of 100 yards had an extreme spread of 0.428". The bullet used was the Berger 85 grain Match Burner.







    Another small 10-shot group fired from a semi-automatic AR-15 at a distance of 100 yards had an extreme spread of 0.474". The group was fired using Sierra 55 grain BlitzKings.





    Both of the groups pictured above were fired from barrels with 1:7.7" twists.


    So find a bullet that your barrel likes, and then you can start making adjustments with different charges of different burning rate powders.

    If you're loading for terminal ballistic properties, that's a whole nother ball game.
    Yes SIR! Thank you!!!

    I would most definitely like to see a similar post precisely about terminal ballistics.

    My predisposition is to always try to make super accurate rounds but I built this SBR precisely to do something different. In other words extreme accuracy is a secondary concern. I would actually say terminal ballistics would be primary actually.

    Again, I don't want to throw out accuracy completely, but terminal ballistics is more what I am aiming for. It would be nice to have the best of both worlds... or a good compromise.

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    Quote Originally Posted by alamo5000 View Post
    I just wonder if a low velocity 75 grain shot would be more destructive than a faster 55 grain...
    Should be able to calculate energy upon impact. Energy = mass x velocity2. Think in terms of 200/300 yards and not 10 ft from the muzzle.

    Quote Originally Posted by alamo5000 View Post
    I have done some google fu and with a standard 55 grain bullet muzzle velocity will be around 2500 fps out of a 10.5 barrel.
    Quote Originally Posted by alamo5000 View Post
    If I go with the 75 grains based on the hogdon reload data and a little bit of guesswork I would be right around 2000 fps.
    I'd be really surprised if there was a 500fps difference between the a 55gr and 77gr.

  11. #11
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    Molon is the man...that's all I gotta say

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    Hell, I could be completely wrong. But I know what I don't know so here I am asking LOL!

    I do understand that under a certain level of velocity projectiles will not expand or perform as intended... so based on my own deductive reasoning if I did create a 77gr load...at the same time I would be decreasing the range where terminal ballistics would be adversely effected.

    I just don't know all those details and I don't want to be wandering around in space forever trying to figure it out.

    If I can shoot 2 inch groups at 100 yards and have effective bad ass terminal ballistics at that range then I am happy with that. For this rifle I don't need dime size groups. That said although the thought of having a heavy load (77gr) sounds on paper to be awesome I still want to know more about the lighter loads too.... 55 gr... 62gr... I am just not sure...

    It's better to ask than to feel around in the dark.

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    Quote Originally Posted by DeviantLogic View Post
    Molon is the man...that's all I gotta say
    ^^^ What he said.

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    Quote Originally Posted by alamo5000 View Post
    It's better to ask than to feel around in the dark.
    Absolutely! I love the thought process in reloading. Trying to think through it along with you :)

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    Quote Originally Posted by DeviantLogic View Post
    Absolutely! I love the thought process in reloading. Trying to think through it along with you :)
    At least my inquisitive nature isn't irritating EVERYONE LOL!!!

    I am just thinking out loud here but if I did create a load with a 77gr bullet ....in a strict measure of terminal ballistics it might only be 'really' effective for 50 or 60 yards. That of course is pure 110% speculation.

    Which I came to that conclusion merely by looking at a ballistics chart with some estimated numbers.

    That then leads me to considering lighter rounds IE 55gr...

    It might be splitting hairs but I want a stable bullet that has good terminal performance and pretty good accuracy out to at least 100 yards.

    I will be using a supressor so I need to take that into account (definitely needs bullet stability) I also will not use a bipod or anything. I have an Aimpoint T2 on the way so my goal here with this set up is to be minute of man. Point and get on target and blast. Accuracy yes, but it is not primary.

    That said if I am ever trying to kill a hostage taker who is standing behind a hostage I want to hit him not her. In other words I will never be in that situation so it won't matter.... but I want to make a load that will do it.

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